what I do Is that I use sharpies and color on to the spot i want to color on but be careful because if your hand starts shaking stop and wait for the shaking to stop or it can ruin the area your customisingPermalink

I went out to the local hobby store and bought model paint, model glue, and a plastic model knife, U can do pretty much anything withe that stuff. O and get a fine model paintbrush too that works great. Permalink

Also you can make custom guns and things if you melt wax and then shape it to how U want with a knife or something and then put it in plaster.
after the plaster is done drying U can melt plastic (I use megablocks) and pour it into the plaster mold, and there you have a custom gun.
Make sure U melt the plastic outside too. Permalink